Generally, in a motor car engine, an oil filter is included in a lubricating system for removing such impurities as worn out metal particles, carbon, etc. However, there is a limit for the filtering ability of the oil filter so that it has been necessary to exchange it at each run of 2,500-3,000 km for ordinary oil and to exchange the filter element at each run of 5,000-6,000 km. More particulary, a conventional filter element has adopted a system in which oil is passed substantially in the direction of the thickness of a single sheet of filter paper so that it is liable to result in clogging. Further, it has been quite impossible to arrest fine particles of carbon, ash component, worn out metal powders or the like of less than 10 microns, particularly water component.
As above described, to discard still substantially usuable lubricating oil merely due to the filtering capability of the oil filter not only contradicts resource saving but also these is a fear of causing a secondary public hazard and a solution of this has been desired. Consequently, it has been considered to use a filter element having a high filtering capability, but when such element is used, the cost generally increases. Furthermore, there is a defect that the size of the oil filter itself becomes large.
Accordingly, in recent years, it has been proposed a filter utilizing a so-called tissue element, that is a filter element prepared by wrapping many times a thin sheet of filter paper about a core body. With this oil filter, although a capability of filtering said fine particles and water component entrained into the oil can be fully expected there are such defects that the filtering efficiency is not high and that the construction is complicated, thus increasing the manufacturing cost. Namely, since the construction is such that the oil passes in the axial direction of the element (a direction parallel to the surface of the wrapped paper) there is a limit for the filtered flow quantity, that since the end surface acting as the inlet side of the oil is narrow when the arrested particles deposit on the surface, filtered flow quantity decreases greatly, and that since the element is tightly fitted in a casing it is necessary to use a special value.